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javascriptreactjsasynchronoususe-effect

Cannot setting the state with the data fetched in useEffect -React


I want to send an API request in useEffect hook and setting the state variables value with the fetched data. I added 2 console.log for detecting the state variables value. I except the second log to be setted with the fetched data, however it still prints null.

Here is my code:

import { useEffect, useState } from "react";
import axios from "axios";
const Test = () =>{
    const [users, setUsers] = useState(null);
    useEffect(()=>{
        const getData = async ()=>{
            const resp = await axios.get("https://jsonplaceholder.typicode.com/todos");
            console.log(users);
            setUsers(resp.data);
            console.log(users);
        };
        getData();
    },[])
    return (
        <div>hello</div>
    )
};

export default Test;

Additionally the console output look likes this:

null
null

Solution

  • useState's setter is asynchronous, therefore your second console.log will be called before the users is actually updated.

    For it to work, just put it outside the useEffect.

    import { useEffect, useState } from "react";
    import axios from "axios";
    const Test = () =>{
        const [users, setUsers] = useState(null);
        useEffect(()=>{
            const getData = async ()=>{
                const resp = await axios.get("https://jsonplaceholder.typicode.com/todos");
                console.log(users);
                setUsers(resp.data);
            };
            getData();
        },[])
        console.log(users);
        return (
            <div>hello</div>
        )
    };
    
    export default Test;
    

    or in another dedicated useEffect, by passing users in the dependencies array.

    import { useEffect, useState } from "react";
    import axios from "axios";
    const Test = () =>{
        const [users, setUsers] = useState(null);
        useEffect(()=>{
            const getData = async ()=>{
                const resp = await axios.get("https://jsonplaceholder.typicode.com/todos");
                console.log(users);
                setUsers(resp.data);
            };
            getData();
        },[])
    
        useEffect(()=>{
           console.log(users);
        },[users])
    
        return (
            <div>hello</div>
        )
    };